Raiders of the Wild Grains
Ancient cereals may hold secrets that address modern challenges
By Becky Beyers
About ten thousand years ago, probably in the area of the Middle East known as the Fertile Crescent, early hunter-gatherers stumbled upon wild cereal species they could domesticate and figured out how to turn these grains into food.
Since then, cereal grains like wheat and barley have been cultivated for yield, for disease resistance and for hardiness, among other things. The 20th century Green Revolution brought that process even further along, adding modern fertilization and growing techniques.
But what might have been lost along the way as cereals became domesticated? CFANS scientists are examining the grains that still grow wild in the Fertile Crescent to see whether they contain genes that, combined with modern domestic varieties, could help feed the world's growing population.
Rich with diversity
Last spring, a group led by Department of Plant Pathology professor Brian Steffenson ('80–B.S., Plant Health Technology; '83–M.S., Plant Pathology) visited colleagues at Tel Aviv University, in part to refresh a 50-year partnership between the universities but also to collect more species that might have traits valuable to modern wheats and barleys.
"Even though it is such a tiny country, Israel is an extremely rich land for genetic diversity of these very important wild progenitor species," Steffenson says. The group on the recent trip was specifically looking for, collecting samples and noting the habitat of four common species of wild grasses.
"It's pretty easy to find them," he says. "Wild barley is everywhere. But some of the wild wheats have a more limited distribution; one of the main things we saw on this trip was threatened habitats where new roads or housing projects had displaced these species."
For example, a wild grass called Sharon goatgrass or Aegilops sharonensis grows mainly along the coastal plain of Israel and into southern Lebanon, a highly urbanized and very narrow strip of land. Not much space is left for the native grasses, Steffenson says.
That particular species has shown excellent resistance to a potentially disastrous threat. "The thing that really surprised us was the very high frequency of resistance to African stem rust in these wild Aegilops accessions," he says. "That was very promising... if we lose these grasses, we'll lose access to their important genes."
Samples of the collected wild cereal grains are stored in the Lieberman gene bank at the Institute for Cereal Crops Improvement at Tel Aviv University. Inside a large cold room, the seeds are stored in bottles and envelopes at 4 degrees Celsius and in low humidity, the optimal conditions for long-term storage.
Steffenson and his colleagues request samples from the gene bank and screen them for resistance to diseases that affect cereal crops in Minnesota and the rest of the world. Once a wild cereal sample is found that shows disease resistance, researchers begin the process of crossing it with wheat or barley. Wild barley can be readily hybridized with cultivated barley, Steffenson says, but creating a new variety of wheat from Aegilops species is a more complex and painstaking process.
Recent technology, however, provides ways to speed up the process, maybe by as much as half. Scientists at the U of M, working with colleagues in the United Kingdom, now can transfer only the key genes from a wild progenitor into an existing wheat variety. None of the wild variety's unwanted genes come along. "We're essentially making evolution go a bit faster by selectively splicing out the genes we want and putting them into an already good wheat variety," Steffenson says. While that may be controversial because it involves the genetic modification of wheat, "it is a technology that really needs to be developed and can benefit mankind greatly. It remains to be seen whether such wheats will be accepted commercially, but we have to investigate the technology."
Along with disease resistance, the scientists are looking at winter hardiness and grain quality. After a new strain is found to combine resistance with other quality traits, the process shifts to CFANS plant breeding experts.
More than disease resistance
In most cases, that plant breeding expert is Jim Anderson, professor in the Department of Agronomy and Plant Genetics.
"The primary motivation for this research is to bring in new resistance genes," he says, "but there is a possible second benefit of genetic diversity." While most of his work involves spring wheats developed specifically for northern climates, "there's gene material that's never been introduced in our work. It's prudent to focus on that diversity."
Beyond disease resistance, Anderson looks for grains with high yield and high protein content. Specific genes in wheat affect the quality of the bread it makes, whether that's water absorption capacity in the dough or loaf volume. "At some level there is genetic control of those traits. And if we can access some of them, we can increase the value of the commodity," he says.
Anderson's process involves crossing and back-crossing varieties he knows can succeed in Minnesota with wild species from Steffenson's work. "The idea is to get rid of more and more of the wild species' genes that we don't want," Anderson says. "At the end of that, we do field tests, hoping to find at least a couple that we want to go forward." But it's a long process. "We have a few varieties in development now that are close to being commercially available from research started years ago. It can be 20 to 25 years from the time the process starts, using such unadapted germplasm until a farmer can buy the seed."
That timespan is one reason the genetic modification techniques offer a good alternative, Steffenson says. "Potentially we could halve the time it takes to do this, if the public will accept genetically modified wheat and see there's a value."
Wild grass samples in other countries in the Fertile Crescent also may have potential for improving cereals on a global scale, but violence and the ever-growing demand for food in that part of the world complicate matters. Steffenson says an international research institute in Aleppo, Syria, was destroyed earlier this year because of the civil war, although reports say germplasm from the gene bank has largely been preserved and moved outside the country. In Turkey, which makes up part of the northern Fertile Crescent region for wild cereal diversity, large domestic wheat fields have taken over many habitats where native grasses once grew.
Steffenson, Anderson and their colleagues are part of a worldwide effort known as the Borlaug Global Rust Initiative, which is funded by the Gates Foundation and includes about 100 scientists from more than 30 institutions, focused on developing new wheats that can resist the deadly rust race called Ug99. They're the primary group in that effort looking at how wild grains might contribute to developing rust-resistant wheat.
But the work goes beyond disease resistance—and beyond wheat and barley. "We're trying to look at it from a comprehensive standpoint," Steffenson says. "We're cataloging the habitats where each species exists and making sure we have comprehensive collections that are preserved and maintained in good quality in the gene banks.
"As a plant pathologist, my first interest is in identifying new genes for disease resistance in these wild species, with special emphasis on the dangerous African stem rust. But I'd like to see other research groups evaluate these wild cereal collections for additional important traits such as tolerance to heat, drought and salinity. If you collect seed and it sits in a gene bank and nobody does anything with it, to me that's not a gene bank, it's more like a gene morgue. The seed might eventually die with nobody doing anything with it."
Modern genome-sequencing tools expand the possibilities, he adds. "It's not unrealistic that we could obtain the complete genome sequence for every one of these accessions; we're just limited by money and personnel. If we could do that for all these species and put it together with bioinformatics tools and identify the genes that control traits like zinc content or disease resistance, that would go a long ways toward enhancing our understanding and ability to breed new varieties that augment these traits."
Similar efforts are happening in other parts of the world, with other crops, Steffenson says. In each case there's a treasure trove of genes that can be exploited from the wild species. The goal is to do this for cereals, potato, soybean, apples—you name it.
"That's the value of so much great genetic diversity. It's going to take a lot of time to go through it all, but we're going to try to take as big a bite as we can."